(Phys.org) —Few catalysts are energy efficient, highly active, stable, and operate in water, but a nickel-based catalyst designed at the Center for Molecular Electrocatalysis at Pacific Northwest National Laboratory quickly ...

Fuel cells that convert hydrogen into power and only produce pure water as a by-product have the potential to lead individual mobility into an environmentally friendly future. The Paul Scherrer Institute (PSI) has been researching ...

(Phys.org) —Scientists and entrepreneurs of old spent millennia trying to transmute lead into gold. Today, a new and more intellectually rigorous kind of alchemy has begun to produce important benefits for an economy that ...

A new cost-effective polymer membrane can decrease the cost of alkaline batteries and fuel cells by allowing the replacement of expensive platinum catalysts without sacrificing important aspects of performance, according ...

A new, computationally-inspired approach has led a team of Boston College chemists to re-conceptualize a highly valued catalytic process, dramatically increasing the efficiency of a chemical transformation that selectively ...

Catalysts are everywhere. They make chemical reactions that normally occur at extremely high temperatures and pressures possible within factories, cars and the comparatively balmy conditions within the human body. Developing ...

A NASA engineer has achieved yet another milestone in his quest to advance an emerging super-black nanotechnology that promises to make spacecraft instruments more sensitive without enlarging their size.

Using a new analytical methodology—a coupled micro-computed X-ray tomography (MicroCT) and microfluidic-based electrochemical analysis—researchers at the University of Illinois at Urbana-Champaign are gaining new insights ...

A breakthrough in our understanding of the properties of titania (titanium dioxide) - the basis of self-cleaning window technology - has been made by scientists at UCL, uncovering a decades old misunderstanding that has clouded ...

Catalysis

Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the activity of catalysts are called promoters and substances that deactivate catalysts are called catalytic poisons. For instance, in the reduction of ethyne to ethene, the catalyst is palladium (Pd) partly "poisoned" with lead(II) acetate (Pb(CH3COO)2). Without the deactivation of the catalyst, the ethene produced will be further reduced to ethane.

The general feature of catalysis is that the catalytic reaction has a lower rate-limiting free energy change to the transition state than the corresponding uncatalyzed reaction, resulting in a larger reaction rate at the same temperature. However, the mechanistic origin of catalysis is complex. Catalysts may affect the reaction environment favorably, e.g. acid catalysts for reactions of carbonyl compounds, form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.

Kinetically, catalytic reactions behave like typical chemical reactions, i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slow step, and rates are limited by amount of catalyst. In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts.

Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid-liquid system or evaporate in a solid-gas system.